Method of forming a stacked device filler

ABSTRACT

Numerous embodiments of a stacked device filler and a method of formation are disclosed. In one embodiment, a method of forming a stacked device filler comprises forming a material layer between two or more substrates of a stacked device, and causing a reaction in at least a portion of the material, wherein the reaction may comprise polymerization, and the material layer may be one or a combination of materials, such as nonconductive polymer materials, for example.

BACKGROUND

[0001] In the manufacture of microelectronic devices, packaging densityis becoming increasingly important. Stacking of the dice of amulti-processor microelectronic device is one way to improve thepackaging density of a microelectronic device. Stacked microelectronicdevices are typically formed by stacking two or more wafers withintegrated circuitry formed thereon, forming bonded wafers, and thendicing the stacked wafers into individual stacked devices. FIG. 5illustrates a stacked microelectronic device 236, which may result fromthe fabrication technique briefly described above. Device 236 comprisesa first microelectronic die 216 having an active surface 218, and anintegrated circuitry layer 222, which contains integrated circuitry notshown in detail. Typically, the integrated circuitry layer is formed toa depth of approximately 10 microns. An interconnect layer 224 is formedon the die 216, and is illustrated as a plurality of interconnectstructures, but may additionally comprise multiple layers of conductivetraces separated by dielectric material (not shown). The interconnectlayer 224 provides routes for electrical communication betweenintegrated circuits, integrated circuit components, and externaldevices, for example.

[0002] Device 236 comprises a second microelectronic die 202, whichadditionally contains an integrated circuitry layer 208 and aninterconnect layer 212. The physical attachment of interconnect layer224 to interconnect layer 212 may electrically interconnect integratedcircuitry layer 222 with integrated circuitry layer 208. Die 202 may bethinned, prior to dicing, and a plurality of conductive vias 228 may beformed on the back surface 226 to be in electrical contact with theintegrated circuitry layer 208. A plurality of solder balls 232 may beformed such that one or more solder balls are in electrical contact withone or more vias. Formation of the plurality of vias 228 and pluralityof solder balls 232 may make it possible to route input/output signals,power, and ground to and from the integrated circuitry layers, forexample.

[0003] Typically, thinning of one of the stacked wafers is performed byuse of one or more mechanical and/or chemical processes, such as apolishing process, for example. These processes may cause mechanicalstresses in the unsupported portions of the wafer being thinned.Unsupported portions of the wafer may include, for example, the areas ofthe wafer not supported by interconnect structures, for example. Thesemechanical stresses may result in undesirable effects such as chipping,cracking, or other mechanical damage, which may result in the waferand/or individual stacked devices being unusable. A need, therefore,exists for a method of forming stacked devices that reduces oreliminates these undesirable effects.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The subject matter regarded as particular embodiments areparticularly pointed out and distinctly claimed in the concludingportion of the specification. Embodiments of the claimed subject matter,however, both as to organization and method of operation, together withobjects, features, and advantages thereof, may best be understood byreference to the following detailed description when read with theaccompanying drawings in which:

[0005]FIG. 1 illustrates several phases of formation of a stacked devicefiller in accordance with at least one embodiment;

[0006]FIG. 2 illustrates several phases of formation of a stacked devicefiller in accordance with at least one embodiment;

[0007]FIG. 3 is a process flow diagram illustrating one method offormation of a stacked device filler in accordance with at least oneembodiment;

[0008]FIG. 4 is a process flow diagram illustrating another method offormation of a stacked device filler in accordance with at least oneembodiment; and

[0009]FIG. 5 is an illustration of stacked microelectronic device, asknown in the art.

DETAILED DESCRIPTION

[0010] Embodiments of the claimed subject matter may comprise a methodof forming a stacked device filler. In one embodiment, a method offorming a stacked device filler comprises forming a material layerbetween two or more substrates of a stacked device, and causing areaction in at least a portion of the material, wherein the reaction maycomprise polymerization and the material layer may be one or acombination of materials, such as nonconductive polymer materials, forexample.

[0011] As mentioned previously, during fabrication of a device such as astacked microelectronic device, one or more fabrication processes maycause mechanical stress in one or more of the stacked wafers, which mayresult in physical damage. One such fabrication process is a thinningprocess, typically performed on one of the stacked wafers prior todicing of the wafers into individual stacked devices. As illustrated inFIG. 5, die 202 is substantially thinner than die 216, but die 202 mayinitially be the same thickness as die 216 when initially assembled intostacked wafers. For example, both die 202 and die 216 may be 700 to 800microns thick prior to dicing and thinning, and die 202 may subsequentlybe thinned to a thickness of 10 to 100 microns, in order to allow forthe formation of conductive vias and provide communications routes forthe stacked device, as explained previously. During the thinningprocess, which may comprise chemical mechanical polishing (CMP),grinding, or a silicon wet etch, for example, unsupported regionsbetween interconnect structures may flex, which may cause portions ofthe die 202 to crack or chip. This physical damage to die 202 may reduceor destroy the functionality of the die, and may additionally causecontaminant incursion, resulting in damage to other dies on the wafer,for example.

[0012] As will be understood by those of skill in the art,microelectronic wafers used in one or more of the following embodimentsmay include any substrate capable of having integrated circuitry formedthereon, including silicon, germanium, indium telluride, or galliumantimonide, to cite just a few examples. Additionally, it will beunderstood that circuitry formed on substrates such as those describedmay be any circuitry, including circuitry used in central processingunits (CPUs), chipsets, memory or application specific integratedcircuits (ASICs). Finally, it will be understood that the individualdies of devices formed in accordance with one or more of the followingembodiments may comprise identical or differing integrated circuits, forexample.

[0013] It is worthy to note that any reference in the specification to“one embodiment” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the claimed subject matter.The appearances of the phrase “in one embodiment” in various places inthe specification are not necessarily all referring to the sameembodiment.

[0014] Numerous specific details may be set forth herein to provide athorough understanding of embodiments of the claimed subject matter. Itwill be understood by those skilled in the art, however, that certainembodiments may be practiced without these specific details. In otherinstances, well-known methods, procedures and components have not beendescribed in detail so as not to obscure the embodiments of the claimedsubject matter. It can be appreciated that the specific structural andfunctional details disclosed herein may be representative and do notnecessarily limit the scope of the claimed subject matter.

[0015] Referring now in detail to the drawings wherein like parts aredesignated by like reference numerals throughout, there is illustratedin FIG. 1, several phases in the formation of a stacked device having afiller, in accordance with at least one embodiment. Stacked device 100comprises two substrates 106, each with a dielectric layer 108 andinterconnect structures 104 formed thereon. Substrates 106 may comprisesemiconductor substrates such as silicon substrates, for example, andmay each comprise a portion of a silicon wafer after patterning ofinterconnects and formation of a dielectric layer, for example.Substrates 106 may have an active surface 112, and one or moreintegrated circuitry layers, which may contain integrated circuitry notshown in detail. Although both are designated similarly as substrates106, the circuitry formed on the substrates 106 may be similar ordiffering, depending on the particular stacked device formed from thesubstrates.

[0016] Typically, the integrated circuitry layer is formed to a depth ofapproximately 10 microns. Formed on the active surfaces 112 ofsubstrates 106 are interconnect structures 104, which may comprise aplurality of copper structures, for example, and although illustrated asa plurality of interconnect structures, they may additionally comprisemultiple layers of conductive traces. Interconnect structures 104, whichmay alternatively be referred to as copper lines, may be raised withrespect to the top surfaces 114 of the dielectric layers 108, in atleast one embodiment. Stacked device 100 may be formed by any number ofwell-known fabrication techniques, but it is important to note that theclaimed subject matter is not limited in this respect. As shown onstacked device 100, portions of the substrates 106 may not bestructurally supported, and, additionally, the interconnect structuresmay be exposed, resulting in oxidation, for example, depending on thetype of material(s) used to form the interconnects.

[0017] Stacked device 101 illustrates an additional phase in theformation of a filler, comprising a first material 126. The firstmaterial 126 may be formed between substrates 106, and may be formed ona portion of the top surface 114 of at least one of the dielectriclayers 108, for example. Formation of the first material may beperformed by any number of methods, but one such method comprisesdiffusion, which may result in a liquid material diffusing into aparticular area. Another method of formation may be mass materialtransport by capillary action, which may result in liquid migratingbetween substrates. In one embodiment, one side of a stacked device,such as opening 110, may be at least partially immersed in a firstmaterial, wherein the first material comprises a liquid. The firstmaterial may migrate at least partially between the substrates bycapillary action, for example, depending on particular materialproperties such as viscosity. Alternatively, the stacked device 101 maybe fully submersed in a first material, and the material maysubsequently flow between the substrates and be deposited on at least aportion of the exposed surfaces of the device, for example. Additionalmethods of formation are in accordance with certain embodiments,explained in more detail hereinafter. Numerous materials or combinationsof materials may be utilized to form the first material 126. Examples ofsuitable materials may include, for example, monomers or monomersolutions, such as a diisocyanate monomers or diisocyanate end-cappedcompliant oligomers, but any material or combination of materials thathave the capability to be formed between two or more substrates of astacked device, and/or exhibit desirable material properties for thepurposes described herein may be used in at least one embodiment.

[0018] Stacked device 103 illustrates an additional phase of formationof a stacked device filler, comprising a second material 128. As shownon stacked device 103, a second material 128 is formed such that it isin contact with at least a portion of the first material 126. Formingthe second material such that the material is in contact with at least aportion of the first material may cause a reaction, such aspolymerization, which may produce outgassing within a polymer matrix,creating a polymer foam, for example, such as a polystyrene, polyester,or polyurethane. The foam material may serve as a filler materialproviding structural support and/or insulation to the stacked device.Forming of second material 128 may comprise a number of methods, butdiffusion or material injection are two examples. Additionally, device103 may be submersed in a material such as a second material, whereinthe second material comprises a liquid. Submersion may cause the secondmaterial 128 to flow at least partially between the substrates and comein contact with the first material 126. Numerous techniques may be usedto deposit a second material, and similarly, numerous materials may beused as a second material. Examples of suitable materials may include,for example, water, hydroxyl end-capped oligomers, carboxylic acidend-capped polymers, or one or more gases. It is important to note,however, that the material or combination of material used as a secondmaterial are not limited to these examples, but may comprise anymaterial(s) that are capable of initiating a reaction, such aspolymerization, and causing a filler material to be formed, and willdepend at least in part on the composition of first material 126.

[0019] Stacked device 105 illustrates an additional phase of formationof a stacked device filler. Device 105 illustrates a fill material 130,formed at least in part from a combination of first material 126 andsecond material 128. The material composition of fill material 130 mayvary depending on the material or combination of materials used as thefirst and second material. Fill material may be a byproduct of areaction between the first material and the second material. Forexample, if a diisocyanate material is used as the first material, watermay be used as a second material, resulting in the formation of apolymer foam as the fill material 130. Similarly, a diisocyanate monomermay be used as first material 126, and may be diffused between thesubstrates 106. A carboxylic acid end capped polyester may then bedeposited on a portion of the first material 126, which causes areaction resulting in the production of polymer foam. Additionalreactions or material combinations may be used to form fill material130, and specific embodiments may be described in more detailhereinafter.

[0020] In an alternative embodiment, a second material 128 is not usedto cause a reaction and result in the production of a fill material 130,but only a first material 126 may be deposited between the substrates106. Depending on the material or combination of materials used as afirst material 126, a reaction may be caused by heating the firstmaterial, or may be caused by introducing the material to a lowerpressure, such as ambient pressure, for example. In this embodiment, apolymer material, such as polystyrene, may have a gas such as nitrogengas dissolved substantially within the polystyrene at a pressure greaterthan ambient, such as 1-2 times greater. This gas may be referred to asa blowing agent. The polymer material may be formed at least partiallybetween two or more substrates, while the pressure greater than ambient.Once formation is substantially complete, the pressure may be allowed toreturn to ambient, and the blowing agent will expand, creating-a polymerfoam. As an additional example of this alternative embodiment, a blowingagent such as p-toluenesulfonyl semicarbazide may be formed between thesubstrates 106, and subsequently heated to a particular temperatureuntil a reaction occurs in at least a portion of the blowing agent.Additionally, a combination of a first and second material, and aheating process or introduction to a gas may be used in otheralternative embodiments.

[0021]FIG. 2 illustrates several phases of formation of a stacked devicefiller in accordance with an additional embodiment. Illustrated in FIG.1 is device 107; which may comprise a substrate 106 with a dielectriclayer 108 and a plurality of interconnect structures formed thereon.Similarly to the substrates illustrated in FIG. 1, substrate 106 maycomprise semiconductor substrate such as silicon substrates, forexample, and may comprise a portion of a silicon wafer after patterningof interconnects and formation of a dielectric layer, for example.Substrate 106 may have an active surface 112, and one or more integratedcircuitry layers, which may contain integrated circuitry not shown indetail. Interconnect structures 104, which may alternatively be referredto as copper lines, may be raised with respect to the top surface 114 ofthe dielectric layer 108.

[0022] Device 109 illustrates an additional phase of formation of oneembodiment of a stacked device filler. Device 109 comprises a substrate106, and a dielectric layer top surface 114 with a material layer 118formed thereon. The material layer 118 may comprise a number ofmaterials or combination of materials, but in two particularembodiments, the material layer may comprise a polymer material, or apolymer material and a blowing agent in combination. Methods of forminga material layer on the dielectric layer top surface may vary, dependingat least in part on the material(s) used as the material layer 118, butone particular method comprising spin coating the material layer 118 onthe dielectric layer top surface to a thickness greater than thethickness of the exposed portions of the interconnect structures 104,for example. Numerous additional methods of forming a material layer 118are in accordance with varying embodiments, as will be explained in moredetail hereinafter.

[0023] Devices 111 comprise two devices such as device 109, which mayhave been formed by use of one or more similar or differing methods,such as those described herein. As shown in devices 111, a portion ofthe material layers 118 have been selectively removed, in order toexpose at least a portion of the interconnect structures 104. Dependingat least in part on the material(s) used as a material layer 118,removal may be a selective removal, and may be accomplished by use of avariety of methods, and may depend at least in part on the type ofmaterial or combination of materials used to form the material layer118. Examples of such methods of removal may comprise a chemicalmechanical polishing process (CMP), which comprises the use of one ormore chemicals and one or more mechanical processes in order to removeparticular portions of a layer of material, for example, or a dryetching process, such as reactive ion etching (RIE), although numerousother methods of removal exist, including grinding or spin etching. Thematerial layer 118 may be selectively removed, or polished back, suchthat at substantial portion one or more of the interconnect structures104 are exposed, and in one particular embodiment, the material layermay be polished back such that the top surface of the material layer isslightly lower than the top surface of one or more interconnectstructures 104, for example.

[0024] Stacked device 113 illustrates two substrates each with adielectric layer, a plurality of interconnect structures and a fillmaterial 132 formed therebetween. The two substrates 106 may be alignedsuch that the interconnect structures are substantially opposing. Theinterconnect structures 104 may then be placed in physical contact, andmay subsequently be bonded, and this may be a result of material creep,for example. In one embodiment, the interconnect structures may bebonded by elevating the temperature of the structures, although, ofcourse, the claimed subject matter is not so limited. After bonding ofthe interconnect structures, a reaction may be caused in the twomaterial layers shown formed on devices 111, which may produce fillmaterial 132. The reaction may be a result of introducing a reactant tothe material layers, such as by diffusing a material between thematerial layers. Additionally, no material may be introduced, but areaction may be caused by elevating the temperature of the materiallayers, or by introducing a gas to the material layers, for example.Methods of forming the fill material 132 may vary, and will be explainedin more detail hereinafter. In one exemplary embodiment, the materiallayers 118 may be formed a polymer precursor with an incorporatedblowing agent, and the material layers 118 may be heated to a particulartemperature after formation, selected such that it results in causing anoutgassing within a polymer matrix, resulting in the production of apolymer foam incorporated between the substrates 106.

[0025]FIG. 3 illustrates a process flow diagram illustrating theprocesses used to form a stacked device with an underfill in accordancewith at least one embodiment. The flowchart 139 illustrated in FIG. 3may be used to substantially perform the phases of formation illustratedin FIG. 1, for example, although the process flow is not limited in thisrespect, and the order in which the functional blocks are presented donot necessarily limit the claimed subject matter to any particularorder, and several intervening functional blocks may be used within thescope of the claimed subject matter. In this embodiment, one or moresubstrates with exposed structures are formed at functional block 140;the one or more substrates are assembled into a stacked device atfunctional block 142; a first material is formed between the substratesat functional block 144; a second material is formed between thesubstrates at functional block 146; and the stacked device is finishedat functional block 148.

[0026] In one embodiment, at functional block 140, formation of one ormore substrates with exposed structures may comprise forming a substratewith a plurality of interconnects, which may comprise a silicon wafer,for example, wherein the silicon wafer may have an active surface withone or more layers of circuitry bonded to the interconnects, forexample, and the circuitry may comprise a CPU, ASIC, or an IntelStrataFlash® memory device, for example. Many methods of formation of asubstrate such as described exist, and the claimed subject matter is notlimited in this respect. A substrate such as illustrated as part ofstacked device 100 of FIG. 1 may be formed by use of one or more ofthese well-known methods, for example.

[0027] In one embodiment, at functional block 142, assembly of thestacked device may comprise placing two or more substrates formed atfunctional block 140 into physical contact, where the interconnectstructures are typically in physical contact. Numerous methods ofassembly of a stacked device may be used, including alignment andbonding of interconnect structures, as described previously, but theclaimed subject matter is not limited to any particular method ofassembly.

[0028] In one embodiment, at functional block 144, forming a firstmaterial may comprise one or more deposition processes that result inthe depositing of one or more layers of a material or combination ofmaterials on a substantial portion of a substrate. However, numerousadditional methods exist, including diffusion, material injection, oneor more spray processes, or submersion of the stacked device, forexample, and may include any method resulting in the formation of afirst material between at least a portion of two or more substrates of astacked device. It is additionally important to note that methods offormation may depend at least in part on the material or combination ofmaterials used to form the first material. Materials may include, forexample, diisocyanates such as diisocyanates monomers or a diisocyanateend-capped compliant oligomer, or blowing agents such asp-toluenesulfonyl semicarbazide, for example. In one particularembodiment, a portion of a stacked device may be immersed in a solutioncontaining diisocyanate monomers, and the solution may diffuse at leastpartially between the substrates.

[0029] In one embodiment, at functional block 146, forming a secondmaterial may comprise one or more deposition processes that result inthe depositing of one or more layers of a material or combination ofmaterials on a substantial portion of a the first material formed atfunctional block 144. However, numerous additional methods exist,including diffusion, material injection, one or more spray processes, orsubmersion of the stacked device, similarly to the formation of thefirst layer. It is important to note that methods of formation maydepend at least in part on the material or combination of materials usedto form the second material, and may also depend at least in part on thematerial or combination of materials used to form the first material.Materials suitable for use as a second layer in particular embodimentsmay include, for example, water or carboxylic acid end-capped polyester,but may include any material or combination thereof that causes areaction, such as polymerization, in at least a portion of the firstmaterial, resulting in the production of a fill material, for example.Additionally, as stated previously, in an alternative embodiment, areaction may be caused in the first material by elevating thetemperature of the first material, in which case a second material wouldnot be used to cause a reaction and produce a fill material.

[0030] In one embodiment, at functional block 148, finishing of thematerial layer may comprise subjecting the material layer to one or morecuring processes, which may entail introducing the substrate with thematerial layer formed thereon to an elevated temperature for aparticular period of time. Methods used for curing may vary, anddepending on the material(s) used to form the material layer, no curingprocess may be performed, for example. Additionally, one or morefinishing processes may include a removal of excess material, such asexcess material used to form the fill material, for example. Methods ofremoval may depend on the composition of the fill material, but mayinclude grinding, chemical mechanical polishing, or dry etching, as justa few examples.

[0031]FIG. 4 illustrates a process flow diagram 159, illustrating theprocesses used to form a stacked device filler in accordance with atleast one embodiment. The flowchart 159 illustrated in FIG. 4 may beused to substantially perform the phases of formation of a stackeddevice as illustrated in FIG. 2, for example, although the orderpresented does not infer a particular order nor limit the process flowto just these discrete functions. In this embodiment, one or moresubstrates with exposed structures are formed at functional block 160; amaterial layer is formed at functional block 162; the material layer ispolished back at functional block 164; two or more substrates are bondedat functional block 166; a reaction is caused in the material layer atfunctional block 168; and the stacked device is finished at functionalblock 170.

[0032] In one embodiment, at functional block 160, formation of one ormore substrates with exposed structures may comprise forming a substratewith a plurality of interconnects, which may comprise a silicon wafer,for example, wherein the silicon wafer may have an active surface withone or more layers of circuitry bonded to the interconnects, forexample, and the circuitry may comprise a CPU, ASIC, or a memory device,for example. Many methods of formation of a substrate such as describedexist, and the claimed subject matter is not limited in this respect. Asubstrate such as illustrated as phase 100 of FIG. 1 may be formed byuse of one or more of these well-known methods, for example.

[0033] In one embodiment, at functional block 162, depositing a materiallayer may comprise one or more deposition processes that result in thedepositing of one or more layers of a material or combination ofmaterials on a substantial portion of a substrate. Such materials mayinclude compliant materials including polymers, or a polymer material incombination with a blowing agent, for example. Methods of depositing thematerial layer may include, for example, spin coating, dip coating, orspray coating, for example, and may depend at least in part on thematerial or combination of materials used to form the material layer. Inone embodiment, the material layer may comprise a polymer, and may bespin coated to a depth at least as great as the thickness of the exposedportion of the interconnect structures formed at functional block 160.

[0034] In one embodiment, at functional block 164, polishing back thematerial layer may comprise selective removal of the material layer byuse of one or more mechanical and/or chemical processes, such as dryetching or a chemical mechanical polishing process, for example. Methodsused for polishing back may depend at least in part on the compositionof the material layer, and may comprise multiple processes, for example.The material layer, in one embodiment, may be selectively removed suchthat the top surface of one or more interconnect structures are exposed,for example, in order to allow for bonding of the interconnects to othersubstrate interconnects. In one embodiment, a portion of a layer ofpolymer may be selectively removed by using a chemical mechanicalpolish, which removes a portion of the polymer layer until the layer isslightly recessed in reference to one or more interconnect structuresformed on the substrate, for example.

[0035] In one embodiment, at functional block 166, bonding thesubstrates, in one embodiment, may comprise placing these interconnectstructures into physical and/or electrical contact, and may compriseapplication of pressure, and or an elevation of temperature to completethe bonding process. The stacked device formed by use of the process asdescribed above may be used as a stacked device with an underfill, forexample.

[0036] In one embodiment, at functional block 168, a reaction may becaused in at least a portion of the material layer formed at functionalblock 162. The method or material used to cause a reaction will dependon the type of material or combination of materials used to form thematerial layer, but may include introducing a gas to the material layer,introducing a liquid to the material layer, or elevating the temperatureof the substrate and material layer, for example. In one particularembodiment, a polymer in combination with a blowing agent may have beenformed on the substrate, and then polymerization and outgassing may beinduced by elevating the temperature of the substrate, for example,resulting in the production of a fill material.

[0037] In one embodiment, at functional block 170, finishing of thematerial layer may comprise subjecting the material layer to one or morecuring processes, which may be introducing substrate with the materiallayer formed thereon to an elevated temperature for a particular periodof time. Methods used for finishing may vary, and depending on thematerial(s) used to form the material layer, may or may not be needed,and may comprise removing excess fill material after a reaction hastaken place, for example.

[0038] It can be appreciated that the embodiments may be applied to theformation of any stacked device filler. Certain features of theembodiments of the claimed subject matter have been illustrated asdescribed herein, however, many modifications, substitutions, changesand equivalents will now occur to those skilled in the art.Additionally, while several functional blocks and relations between themhave been described in detail, it is contemplated by those of skill inthe art that several of the operations may be performed without the useof the others, or additional functions or relationships betweenfunctions may be established and still remain in accordance with theclaimed subject matter. It is, therefore, to be understood that theappended claims are intended to cover all such modifications and changesas fall within the true spirit of the embodiments of the claimed subjectmatter.

1. A method of forming a stacked device filler, comprising: forming alayer of first material between two substrates of a stacked device;forming a layer of second material between the two substrates of thestacked device, wherein the second material causes a reaction in aportion of the first material.
 2. The method of claim 1, wherein thereaction comprises polymerization.
 3. The method of claim 1, whereinsaid forming the layer of first material comprises diffusing the firstmaterial between a portion of the two substrates of the stacked device.4. The method of claim 3, wherein the first material is selected fromthe group consisting of: diisocyanate monomers, a diisocyanateend-capped compliant oligomer, and p-toluenesulfonyl semicarbazide. 5.The method of claim 1, wherein said forming the layer of first materialcomprises one or more of: injecting the first material between a portionof the two substrates of the stacked device, spraying the first materialbetween the portion of the two substrates of the stacked device, orimmersing the two substrates of the stacked device in the firstmaterial.
 6. The method of claim 1, wherein forming the layer of secondmaterial comprises diffusing the second material between a portion ofthe two substrates of the stacked device.
 7. The method of claim 6,wherein the second material is selected from the group consisting of:water, a hydroxyl end-capped oligomer, and a carboxylic acid end-cappedpolymer.
 8. The method of claim 1, wherein said forming the layer ofsecond material comprises one or more of: injecting the second materialbetween a portion of the two substrates of the stacked device, sprayingthe second material between the portion of the two substrates of thestacked device, or immersing the two substrates of the stacked device inthe second material.
 9. The method of claim 1, wherein the reactionproduces a polymer foam.
 10. A method of forming a stacked semiconductordevice, comprising: forming a layer of material on a portion of the topsurface of a substrate, said substrate having an interconnect structureformed thereon; selectively removing a portion of the layer of materialto expose a portion of a top surface of the interconnect structure;combining the substrate with another substrate to form a stackedsemiconductor device; causing a reaction in a portion of the layer ofmaterial wherein a portion of the area between the two substrates isfilled with a polymer foam as a product of the reaction.
 11. The methodof claim 10, wherein the reaction comprises polymerization.
 12. Themethod of claim 10, wherein said forming comprises spin coating.
 13. Themethod of claim 12, wherein the layer of material is spin coated to athickness greater than the top surface of the interconnect structure.14. The method of claim 10, wherein the selective removing comprises oneor more of: chemical etch, dry etch, or mechanical etch.
 15. (Canceled)16. The method of claim 10, wherein the layer material is selected fromthe group consisting of: water, hydroxyl end-capped oligomers, andcarboxylic acid end-capped polymers.
 17. (Canceled)
 18. A stackedmicroelectronic device, comprising: a first substrate of silicon, saidsubstrate having a top surface; a plurality of interconnect structuresformed on at least a portion of the substrate; a layer of materialformed on at least a portion of the top surface of the substrate ofsilicon; a second substrate of silicon with a plurality of interconnectstructures formed thereon, said first and second substate interconnectstructures configured such that at least a portion of the interconnectstructures of said first and second substrate respectively are inphysical contact.
 19. The apparatus of claim 18, wherein the layer ofmaterial substantially comprises a polymer foam.
 20. The apparatus ofclaim 19, wherein the polymer foam comprises one or more of:polystyrene, polyester, and polyurethane.
 21. The apparatus of claim 18,wherein the layer of material substantially comprises one or more of:diisocyanate monomers, a diisocyanate end-capped compliant oligomer, andp-toluenesulfonyl semicarbazide.
 22. The apparatus of claim 18, whereinthe layer of material substantially comprises one of: water, a hydroxylend-capped oligomer, and a carboxylic acid end-capped polymer.
 23. Theapparatus of claim 18, wherein the apparatus comprises a stackedchipset.
 24. The apparatus of claim 18, wherein the first and secondsubstrates comprise integrated circuits.
 25. The apparatus of claim 18,wherein at least a portion of the interconnect structures comprisecopper vias.
 26. A method of forming a stacked device filler,comprising: forming a layer of material between two substrates of astacked device; and reacting a portion of the layer of material, whereinthe reaction results in the portion of the layer of material increasingin volume.
 27. The method of claim 26, wherein the reaction comprisespolymerization.
 28. (Canceled)
 29. The method of claim 27, wherein thereaction produces a polymer foam.
 30. A method comprising: depositing afirst material between two substrates of a stacked device; depositing asecond material between the two substrates of the stacked device;wherein a reaction between the first material and the second materialfills a portion of the area between the two substrates with a polymerfoam as a product of the reaction.
 31. The method of claim 30, whereindepositing the first material comprises one of: diffusing the firstmaterial into a portion of the area between the two substrates;injecting the first material into the portion of the area between thetwo substrates; spraying the first material into the portion of the areabetween the two substrates; and immersing the two substrates in thefirst material.
 32. The method of claim 30, wherein the first materialis selected from the group consisting of diisocyanate monomers, adiisocyanate end-capped compliant oligomer, and p-toluenesulfonylsemicarbazide.
 33. The method of claim 30 wherein depositing the secondmaterial comprises one of: diffusing the second material into a portionof the area between the two substrates; injecting the second materialinto the portion of the area between the two substrates; spraying thesecond material into the portion of the area between the two substrates;and immersing the two substrates in the second material.
 34. The methodof claim 30, wherein the second material is selected from the groupconsisting of water, a hydroxyl end-capped oligomer, and a carboxylicacid end-capped polymer.